In the field of the production by rolling of long products such as bars, rods, wire rods, etc. the great competition between the producers entails more and more the need to meet very strict processing parameters in obtaining products of a high quality at ever lower costs and with ever shorter times.
To be more exact, the requirements of the steelmakers as directed to the designers of plants concern the possibility of meeting the following specifications:
dimensional tolerances in a range between .+-.0.08 mm. and .+-.0.1 mm. over the whole range of dimensions of the rolled product (this range of dimensions in this type of plant being generally between 4.0 and 25 mm.); PA1 a speed of finishing of the product higher than 120 mts/sec. and even as high as 140 mts/sec.; PA1 a speed of production of the line at least equal to 120 tons/hr.; PA1 a percentage of discarded material not greater than 3%; PA1 a factor of plant usage at least equal to 90%; PA1 the ability to carry out a finishing process at a low temperature on the whole range of products so as to obtain a high surface and inner quality of the finished product.
All these specifications are not normally met as a whole in the conventional rolling plants, or at least are not met over the whole ranges of products which can be produced by the line.
This situation is due to a plurality of causes which arise mainly from the arrangement of the lay-out of the plant and from the rolling methods conventionally employed, particularly in the change from one dimensional range of products to another.
The rolling method in the conventional plants, which includes a great number of specialised finishing passes for each type of section, entails the necessity of performing frequent and long processes for the change of equipment, and these processes involve long times and the use of labour, thus reducing the factor of exploitation and therefore the efficiency of the plant.
Moreover, in the conventional rolling plants the necessity of performing in separate steps the cropping of the spirals of the leading and trailing ends of the coil entails the use of additional personnel with a resulting increase in costs and in working times for the completion of the process.
Moreover, the conventional rolling method causes the necessity of discarding a great quantity of material, and this situation is now unacceptable in the present rolling plants.
All these problems have induced the present applicants to design a rolling line suitable to meet the above specifications by providing an improved rolling method which improves the characteristics of exploitation and efficiency of the rolling plant, thus achieving a great financial advantage in the production of rolled steels together with quality levels and the ability to repeat those qualities hitherto unattainable in conventional plants.
For this purpose the present applicants have designed, tested and embodied this invention.
This invention is set forth and characterised in the respective main claims, while the dependent claims describe variants of the idea of the main embodiment.
The purpose of the invention is to obtain an improved rolling method and also a rolling line which performs this improved method, the method and the line being such as will optimise the efficiency of a plant performing the rolling of long products, at the same time enabling a product to be made of a high surface and inner quality which is characterised by very small dimensional tolerances.
Another purpose of the invention is to provide an optimised line suitable to work on the whole range of products with shorter and faster operations for the change of equipment, with less use of manual labour and therefore a saving of the labour force and with an improved logistical occupation of space.